In Positron Emission Tomography (PET), and other nuclear medical imaging systems, the detection of 511 keV Gamma radiation caused by the decay of positron emitting radioisotopes with the body of a subject is reconstructed into an image. To perform this accurately it is beneficial to know the spatially dependent absorption of ionizing radiation within the subject.
Combined Computed Tomography (CT) and PET scanners have been constructed which use a low-dose CT to determine the attenuation factors at 511 keV. These scanners have the disadvantage of exposing subjects to radiation while performing a CT examination.
Combined Magnetic Resonance Imaging (MRI) and PET scanners have also been constructed. The journal article Eiber et. al. “Value of a Dixon-based MR/PET attenuation correction sequence for the localization and evaluation of PET-positive lesions” Eur J Nucl Med Mol Imaging (2011), vol. 38, pages 1691-1701, discloses the use of Dixon based MRI imaging techniques for attenuation correction for PET.